Volume 88, Issue 3, September (2002), pp. 325-329 © The Author 2002
doi:10.1079/

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Measurement of total body water using ²H dilution: impact of different calculations for determining body fat

J. LaForgia^1*, R. T. Withers^2
1School of Pharmaceutical, Molecular and Biomedical Sciences, University of South Australia, GPO Box 2471, Adelaide, South Australia 5001, Australia
²Exercise Physiology Laboratory, School of Education, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia

 (Received 3 September 2001–Revised 26 March 2002–Accepted 22 April 2002)

This study estimated total body water (TBW) in four groups (twelve per group; sedentary and highly trained men and women) at the time of ²H dosing (T₀) and after a 3·5 h equilibration period (T_eq). Standard TBW calculations were employed at T₀ (no correction for disproportionate urinary tracer loss) and T_eq (correction for urinary tracer loss only), plus those calculations that corrected for a disproportionate urinary tracer loss and insensible tracer loss respectively. The measurement of body density enabled the four TBW estimates to be compared for the determination of three-compartment % body fat (BF). The very small difference between the standard and corrected T₀ TBW data was not significant (P=0·914) and no Group×TBW interaction was identified (P=0·125). These results reflect the closeness of the ²H concentration in the urine produced during the equilibration period and the T_eq saliva samples. The associated mean % BF values were essentially identical. Although correcting for insensible ²H losses in addition to urinary losses at T_eq produced a statistically significant (P<0·001) lower mean TBW (about 200 g) than the standard calculation, this translated to a small difference in % BF (0·3). The larger difference (about 500 g, P<0·001) between the two (T₀, T_eq) corrected TBW calculations was also associated with a small body composition difference (0·1 % BF), which was less than the propagated error (0·3 % BF) for the three-compartment body composition model. Corrections to the standard calculations of TBW at T₀ and T_eq for a protocol employing a brief equilibration period (3·5 h) were therefore of marginal use for improving the accuracy of % BF estimates. The TBW difference over time (T₀ v. T_eq) also had little impact on % BF values.

Keywords:
Hydrometry: Isotopic dilution: Multicompartment body composition model